CLA: Conjugated Linoleic Acid Research

A deficiency of CLA in the diet may be a major factor in causing Americans to gain so many fat pounds. CLA is a potent antioxidant.

Conjugated linoleic acid (CLA) is a mixture of different types of isomers of linoleic acid, primarily position and geometric isomers, which is found preferentially in dairy products and meat [1]. CLA is supplement that many have heard of but do not know much about. Current research findings suggest that CLA has a number of benefits for bodybuilders as well as any type of athlete. Conjugated linoleic acid is also unique because it is present in food from animal and dairy sources, and its anti-cancer efficacy is expressed at concentrations close to human consumption levels.

Background Information and Benefits of CLA

Conjugated Linoleic Acid is a slightly altered form of linoleic acid (LA), an omega-6 fatty acid important to human health. Omega-6 fatty acids are derived from the foods we eat primarily from meat and dairy products [13]. Therefore, CLA is primarily found in meat and diary products.

Scientific interest in CLA was first stimulated in 1988 when a University of Wisconsin researcher discovered its cancer-fighting properties in a study of rats fed fried hamburger [8]. CLA cannot be produced by the human body, but it can be obtained through foods such as whole milk, butter, beef, and lamb.

Conjugated linoleic acid (CLA) is a potent anti-oxidant, anti-carcinogen, and anti-catabolite, as well as a powerful immune system enhancer [1]. Some of the common accolades of CLA are assistance in fat burning, building and retention of lean muscle, and is a cancer fighter.

Some of the most known suggested benefits of CLA supplementation include:

Increased metabolic rate: This would obviously be a positive benefit for any type of athlete that is trying to lose weight and improve body composition.

Enhanced muscle growth: Muscle burns fat, which also contributes to increased metabolism, which is useful in weight loss and management.

Lowers cholesterol and triglycerides: Since many people these days have elevated cholesterol and triglyceride levels, even with treatment, this benefit can have an impact on any person who has high cholesterol.

Lowers insulin resistance: Lowering insulin resistance has been shown to help prevent adult-onset diabetes and make it easier to control weight.

Reduces food-induced allergic reactions: Since food allergies can be at play when weight loss becomes difficult, this can be of help.

Enhances immune system: With the variety of bacteria and poor immune systems in contemporary society, enhancing the immune system's ability to function properly is a positive benefit to all.

CLA supplementation was also shown to improve the lean mass to body fat ratio, decreasing fat deposition, especially on the abdomen, and enhancing muscle growth. CLA achieves this reaction by it reduces body fat by enhancing insulin sensitivity so that fatty acids and glucose can pass through muscle cell membranes and away from fat tissue [2]. This results in an improved muscle to fat ratio.

Compelling evidence also indicates that CLA can promote youthful metabolic function and reduce body fat. The unique mechanism by which this fatty acid protects against disease makes it an important addition to any supplement program.

Contemporary American society is one that is arguably different than previous generations. Contemporary Americans are generally deficient in consumption of CLA, which is mostly due to the changes that have occurred in the practices of feeding cattle. Since CLA comes primarily from meat and dairy products, changes in the feeding habits of cattle would have a great impact on CLA, which have led to a decline in the content of CLA in meat and dairy products.

For optimal CLA production, cows need to graze on grass rather than be artificially fattened in feed lots [19]. Studies and research findings have shown that the meat form grass-fed cows contain up to four times as much CLA as their non-grass-fed counterparts [15]. Today's dairy products have only about one third of the CLA content they used to have before 1960 [15].

As any person walking down the street in America can see, we have an obesity epidemic in this country. Now I am not saying that CLA is America's savior for fighting obesity but American's deficiency in CLA could have an influence. Several animal studies showed that adding CLA to the diet resulted in leaner, more muscular bodies. One 1996 study, for instance, showed as much as 58% lower body fat in CLA-supplemented mice [6].

As mentioned earlier, CLA is a component of red meat that has been shown to prevent cancer. The FDA has also published research attesting to the anti-cancer properties of CLA [12]. CLA is used by body builders to drive glucose into muscle cells to produce anabolic effects. Dieters can use this same sugar burning mechanism to prevent serum glucose from turning into body fat. The new CLA oil is about 50% stronger in the cis-9, trans-11, isomer, which is considered the best by scientists [2].

CLA is also chemically related to linoleic acid, but appears to have opposite effects in certain important areas. For instance, linoleic acid stimulates fat formation, which is commonly known as lipogenesis, in adipose tissue, while research suggests that CLA inhibits fat formation. Another difference lies in tumor formation; linoleic acid tends to promote tumor growth, while research suggests that CLA is a great inhibitor of tumor development.

Finally another difference lies in that linoleic acid makes cholesterol more susceptible to oxidation, while CLA makes cholesterol more stable [7]. Due to the enormous impact that fatty acids have on our physiology, an excess of linoleic acid combined with a deficiency of CLA could have far-reaching effects on health and longevity.


Recently CLA has also become available in concentrated dietary supplement form. There have been many claims for this supplement, including assertions that it can help burn fat, build muscle, and fight cancer. Although there has been promising research done over the past few decades, it has primarily been in small animals, yet there have been some human studies. It is unclear whether humans will experience the same benefits, however. Findings have been mixed.

In an exciting study done so far, a team of Swedish researchers reported in December, 2000 that CLA takes away fat while increasing muscle mass. The overweight and obese participants in the study experienced a reduction in body fat while taking 3.4 grams of CLA daily for 64 days. Yet the studies yielded none of subjects losing weight. Many of the participants complained of nausea and of the difficulty in taking 12 capsules daily. Only 47 of the 60 participants completed the trial [14].

In another study, a double-blind, randomized, placebo-controlled study was published in the December 2000 issue of the Journal of Nutrition found that CLA reduces fat and preserves muscle tissue. According to the research project manager, an average reduction of six pounds of body fat was found in the group that took CLA, compared to a placebo group.

The study found that approximately 3.4 grams of CLA per day is the level needed to obtain the beneficial effects of CLA on body fat. Dr. Michael Pariza, who conducted research on CLA with the University of Wisconsin-Madison, reported in August 2000 to the American Chemical Society that "It doesn't make a big fat cell get little. What it rather does is keep a little fat cell from getting big.[4]"

Pariza's research did not find weight loss in his group of 71 overweight people, but what he did find was that when the dieters stopped dieting, and gained back weight, those taking CLA "were more likely to gain muscle and not fat.[4]'' In a separate study conducted at Purdue University in Indiana, CLA was found to improve insulin levels in about two-thirds of diabetic patients, and moderately reduced the blood glucose level and triglyceride levels.

In another major trial, researchers from Norway studied a group of healthy but overweight men and women, who were given 1.7g, 3.4g, 5.1g, or 6.8g of conjugated linoleic acid (CLA) per day [11]. All groups showed significant reduction in body fat and increase in lean muscle, but this effect was most significant for the two latter groups. It was also observed that all groups showed a reduction in blood fat and cholesterol.

Subsequently, Swedish researchers studied 25 obese men aged 39-64 for four weeks and found that those taking 4.2g of conjugated linoleic acid per day showed an average loss in waist circumference of 1.4 cm [9].

In a different double-blind study, subjects took part in an exercise program in which they received 600 mg of CLA or a placebo three times per day for 12 weeks. Compared with the placebo, CLA showed a reduction in body fat percentage, but did not significantly reduce body weight [12]. In a double-blind study of obese men, supplementing with 4.2 grams of CLA per day for four weeks produced a small but statistically significant reduction in waist size. However, compared with the placebo, CLA did not promote weight loss. At present, there is not sufficient evidence to support the use of CLA as a treatment for obesity [3].

Animal research suggests an effect of CLA supplementation on reducing body fat. Limited controlled human research found 5.6-7.2 grams per day of CLA produced no significant gains in muscle size and strength in experienced[10] and inexperienced[12] weight-training men[1]. Animal research also suggests an effect of CLA supplementation on limiting food allergy reactions, preventing atherosclerosis, and improving glucose tolerance. As with the cancer research, the effect of CLA on these conditions in humans remains unclear.

Even though there has been a number of positive research finding regarding CLA, there are also a large number of more recent studies that have failed to demonstrate any real significant benefits of supplementation with CLA, as mentioned before.

For example, a study of experienced resistance trainers taking 6g per day of supplemental CLA carried out last year failed to find any significant beneficial changes in total body mass, fat-free mass, fat mass, % body fat, bone mass, strength, serum substrates or general markers of catabolism and immunity during training [14]. Meanwhile, earlier this year, a three-month double-blind placebo-controlled study failed to find any improvement in body weight maintenance after a period of weight loss [16]. Interestingly, however, conjugated linoleic acid (CLA) seemed to aid the preferential regain of fat-free mass at both experimental doses of 1.8 and 3.6g per day [16].

As with the majority of performance-enhancing supplements available today, there is mixed research findings with them. Yet it is also very common that while one product works for one person, it may not work for another so one must experiment themselves and find the proper supplements that help them achieve their goals and works with their body chemistry.

Where Can I Find CLA Naturally?

As mentioned earlier, CLA is found mainly in dairy products and also in red meat, poultry, eggs, and, surprisingly enough, corn oil. There is also bacteria that lives in the intestine of humans that is able to produce CLA from linoleic acid, but supplementation of a rich source of linoleic acid did not product increases in blood levels of CLA in human study. [17] CLA is also available as a supplement. The table bellows shows the amount of CLA is common foods.

Conjugated Linoleic Acid content of common foods [5]

FOOD Typical mgs of CLA per gram of total fat % of CLA present as c9, t11 isomer
Lamb 5.6 92
Homogenized cow's milk 5.5 92
Homogenized cow's milk 4.8 84
Butter 4.7 88
Cottage cheese 4.5 83
Fresh ground beef 4.3 85
Sharp cheddar cheese 3.6 93
Chicken 0.9 84
Pork 0.6 82

Side Effects

The side effects of CLA are unknown, due to the limited research in humans especially the long-term effects. However, one unpublished human trial reported isolated cases of gastrointestinal upset. [17]. At this time, there have been no significant side effects with the use of CLA and there were no well-known drug interactions with CLA.


Conjugated linoleic acid (CLA) is a potent anti-oxidant, anti-carcinogen, and anti-catabolite, as well as a powerful immune system enhancer. A deficiency of CLA in the diet may be a major factor in causing Americans to gain so many fat pounds. CLA is a potent anti-oxidant, but appears to prevent cancer via other mechanisms of action.

Yet there is no point in trying to increase your dietary CLA naturally because, even if all the theoretical benefits were confirmed, a person would have to consume at least 500g of fat, mostly saturated, each day to get meaningful amounts, which is at least three grams. That is over 4,500 fat calories each day just from eat CLA rich foods [11]. Therefore if you want to boost your conjugated CLA intake to the levels used in scientific studies, you must use CLA supplementation.

In regards to CLA supplementation, it would be wise to use those whose isomer content is similar to naturally occurring CLA such as those consistently predominant of c9, t11 CLA, which are ones that are generally found in CLA that is available in stores.

While the t10, c12 [20] isomer may exert a much more potent fat-reducing effect, there are simply too many unanswered questions over its possible health risks to recommend using large amounts at present time. Since CLA is similar to essential fatty acids, it would probably also be wise to make sure you dietary fats are up to par through foods such as sunflower seeds, almonds, peanuts, or EFA supplementation.

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